The invention is based on a tube-forming apparatus in a bag-forming, filling, and sealing machine. In known tube-forming apparatuses of this type, the superposed edge regions of the packing material band are heated by heating belts, jaws, or rollers resting against their outsides, wherein the heat transmitted penetrates through the outer layer into the inner layer. By virtue of the fact that in order to transmit heat into the inner layer, the outer layer must also be heated, a high heating capacity is required on the one hand and a long heating time is required on the other. This is particularly disadvantageous in relatively thick, multi-layer packing materials. For this case, endless heating belts must have a reasonably large contact section, which is accompanied by the disadvantage that the returning part of the belt cools and therefore experiences heat stresses or must also be unnecessarily heated. Heating rollers are not considered since the necessary heat quantity cannot be transmitted in the narrow contact area.
The tube-forming apparatus according to the invention has the advantage that with direct transmission of the heat to the inside of the edge regions of the packing material band to be sealed, the heating capacity of the heating body is low and therefore the contact area is relatively small. If the outside of the edge regions of the packing material belt is also heated, this produces a particularly short structural length of the longitudinal seam sealing device.